Stratigraphical and sedimentological controls on the distribution of Cloudina bioclastic accumulations in the terminal Ediacaran Tamengo Formation (Corumbá Group), Brazil

Abstract

The appearance of the early biomineralized skeletons during the latest Ediacaran was one of the most important evolutionary gains for the ancient animals' lineage. This evolutionary innovation likely represents a pivotal shift in ecology and the interactions between the geosphere and biosphere. Among these fossils, Cloudina stands out as the oldest macroscopic biomineralized metazoan that achieved widespread distribution. However, the complex interplay between sedimentation, preservation, and the vertical distribution of bioclastic accumulations in the Ediacaran strata remains unexplored. The Ediacaran Tamengo Formation (Western Brazil) records thick shallow water deposits and preserves several stratigraphic intervals that contain bioclastic-rich beds formed by Cloudina remains. This unit represents a window for investigating the role of the earliest truly and their impact on Ediacaran marine environments. Our investigation aims to examine the sedimentology and taphonomy of Cloudina within the Tamengo Formation in Brazil to test the hypothesis that the emergence of skeletal hard parts influenced sedimentary depositional processes. To achieve this goal, we combine bioclastic remains and facies/microfacies analysis, taphonomy, and sequence stratigraphy. Our approach involves analyzing the distribution of bioclasts in correlation with stratigraphy and microfacies. By doing so, we aim to forecast the presence of bioclastic accumulations across a mixed siliciclastic–carbonate ramp section. Our findings reveal variability in bioclast sizes among different sites, suggesting a correlation with environmental factors. Furthermore, our study underscores the significance of comparing bioclast accumulations between Precambrian and Phanerozoic deposits, emphasizing their broad utility in understanding evolutionary and environmental shifts over time.